1. Field of the Invention
The invention relates to a battery management system including a plurality of battery cells in a battery pack in which a wireless battery area network is automatically established between a base station (M-BMU) and a plurality of slave battery cell sensor nodes (S-BMU).
2. Description of Related Art
Lithium-ion (Li-ion) batteries are growing in popularity as energy storage reservoirs for industrial and automotive applications, high-voltage energy uses (smart grid), such as wind turbines, photo-voltaic cells, and hybrid electric vehicles, and this has spurred demand for safer, higher performing battery monitoring and protection systems. Compared to NiMH (nickel-metal hydride) battery management systems, see, for example, US. Pat. No. 6,351,097, Li-ion batteries have better energy-to-weight ratio, offer more efficient storage capacity over multiple charge-discharge cycles, and suffer less charge leakage when not in use. Unlike NiMH batteries traditionally used in high-voltage applications, battery stacks using Li-Ion technology can comprise a large number of individual cells totaling hundreds of cells at different voltages. Each cell must be properly monitored and balanced to ensure user safety, improve battery performance and extend battery life. Therefore, the battery management system (BMS) is one of critical components for small and large-scaled battery applications. Examples of Li-ion battery packs are disclosed in U.S. Pat. Nos. 5,602,460; 5,631,537; and 5,646,508. The main objectives of a BMS are: (1) to guarantee appropriate use of the battery, (2) to guarantee maximum performance of the battery, (3) to monitor necessary battery state data, and (4) to permit diagnosis. The BMS architecture should overcome the three major hurdles of state-of-the-art Li-Ion batteries: life cycle, cost and scalability. For example, in Smart Grid and power plant applications, the battery capacity needs to be as large as a few hundred kWh to a few MWh. However, current BMS architecture is not scalable to handle such a large number of battery cells. More importantly, the complexity and cost of wire harnesses for handling large-scaled battery applications is often not acceptable. Also, conventional battery management systems require data bus isolators such as an opto-coupler based vertical bus, and suffer from high cost and high power consumption. Most research efforts have been focused on improving the cell chemistry aspects. Considering that roughly 30% of the cost of a battery pack is for the BMS and the percentage increases as the battery capacity becomes larger, BMS can be a source of significant cost reduction especially for large-scale Li-Ion battery packs. Very few prior art battery management systems use wireless communication, instead of wired media, or a combination of wired and wireless.
U.S. Pat. No. 6,351,097 describes a battery management system for Ni—Cd and NiMH, while the following U.S. Patents discuss possibly relevant battery management systems for Li-Ion or Li-Polymer batteries: U.S. Pat. Nos. 5,963,019; 7,619,417; 7,888,912; 8,022,669; and US 2007/0029972. A useful discussion of secondary battery reuse and protection is found in U.S. Pat. No. 7,710,073.
Lastly, the following U.S. Patents are cited for their useful discussions of the current state-of-the-art of wireless communication in battery management systems: U.S. Pat. Nos. 7,598,880; 7,774,151; and US 2006/0152190.